#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <algorithm>
#include <bitset>
#include <cstring>
#include <vector>
using namespace std;
const int N = 2505;
int dzaxic[N][N];
int ajic[N][N];
int a[N][N];
int n, m;
int M[N];
int mnw = 1000 * 1000 * 1000 + 5;
int mnh = mnw;
vector<pair<int, int> > v;
int main(){
ios_base::sync_with_stdio(false);
cin >> n >> m;
for (int i = 1; i <= n; i++){
for (int j = 1; j <= m; j++){
char c;
cin >> c;
a[i][j] = c - '0';
}
}
for (int i = 1; i <= n; i++)
{
int now = 0;
for (int j = 1; j <= m; j++){
if (a[i][j]){
now++;
dzaxic[i][j] = now;
}
else{
if (now) mnw = min(mnw, now);
now = 0;
}
}
if (now) mnw = min(mnw, now);
now = 0;
for (int j = m; j >= 1; j--){
if (a[i][j]){
now++;
ajic[i][j] = now;
}
else{
if (now) mnw = min(mnw, now);
now = 0;
}
}
if (now) mnw = min(mnw, now);
now = 0;
}
for (int j = 1; j <= m; j++){
int now = 0;
for (int i = 1; i <= n; i++){
if (a[i][j]){
now++;
}
else{
if (now) mnh = min(mnh, now);
now = 0;
}
}
if (now) mnh = min(mnh, now);
}
//cout << mnh << " " << mnw << endl;
/*for (int i = 1; i <= n; i++){
for (int j = 1; j <= m; j++){
cout <<ajic[i][j] << " ";
}
cout << endl;
}*/
for (int i = 1; i <= n; i++){
for (int j = 1; j <= m; j++){
/*if (i == 9 && j == 10){
cout << 0 << endl;
}*/
if (a[i][j] == 1 && a[i - 1][j] == 0 && a[i][j - 1] == 0 && a[i - 1][j - 1] == 0){
int now = -1;
//calc1(i, j, 1);
for (int ii = i; ii <= n; ii++){
if (a[ii][j] == 0) break;
if (now == -1 || ajic[ii][j] < now){
now = ajic[ii][j];
}
now = min(now, mnw);
v.push_back({ ii - i + 1, now });
if (ii - i + 1 >= mnh) break;
}
}
if (a[i][j] == 1 && a[i][j - 1] == 0 && a[i + 1][j - 1] == 0 && a[i+1][j] == 0){
int now = -1;
//calc1(i, j, -1);
for (int ii = i; ii >= 1; ii--){
if (a[ii][j] == 0) break;
if (now == -1 || ajic[ii][j] < now){
now = ajic[ii][j];
}
now = min(now, mnw);
v.push_back({ i - ii + 1, now });
if (i - ii + 1 >= mnh) break;
}
}
if (a[i][j] == 1 && a[i - 1][j] == 0 && a[i][j + 1] == 0 && a[i - 1][j + 1] == 0){
int now = -1;
for (int ii = i; ii <= n; ii++){
if (a[ii][j] == 0) break;
if (now == -1 || dzaxic[ii][j] < now){
now = dzaxic[ii][j];
}
now = min(now, mnw);
v.push_back({ ii - i + 1, now });
if (ii - i + 1 >= mnh) break;
}
}
if (a[i][j] == 1 && a[i + 1][j] == 0 && a[i][j + 1] == 0 && a[i + 1][j + 1] == 0){
int now = -1;
for (int ii = i; ii >= 1; ii--){
if (a[ii][j] == 0) break;
if (now == -1 || dzaxic[ii][j] < now){
now = dzaxic[ii][j];
}
now = min(now, mnw);
v.push_back({ i - ii + 1, now });
if (i - ii + 1 >= mnh) break;
}
}
}
}
// cout << mnh << " " << mnw << endl;
memset(M, -1, sizeof M);
for (int i = 0; i < v.size(); i++){
int a = v[i].first;
int b = v[i].second;
b = min(b, mnw);
if (M[a] == -1 || M[a] > b){
M[a] = b;
}
//cout << a << " " << b << endl;
}
int ans = 0;
for (int i = 0; i < v.size(); i++){
int a = v[i].first;
//a = min(a, mnh);
//if (a > mnh) continue;
int b = M[a];
a *= b;
ans = max(ans, a);
}
cout << ans << endl;
return 0;
}
